Optical studies of color centers in LiYF4:Nd3+ crystals

The synthetic monocrystal of the structure scheelite, LiYF4, doped with rare-earth ions, thrice ionized, Nd3+, was submitted to radiation-X at room temperature. The damage produced by the radiation was studied by techniques of optic spectrograph of absorption and emission. The band of optic absorption centered in 3.70 eV is proposed as being due to the Center F (electron imprisoned in the vacancy of the fluorine ion), not presenting dislocation of energy with the polarization of the light, thus indicating a configuration of high spacial symmetry. Through a criogenic system it was possible to verify the dependence of the profile of this band of absorption with the temperature. Up to temperatures on the order of 200 K, this band can be adjusted to one gauss indicating a strong interaction electron-phonon of the electron imprisoned in this color center. A strong resemblance with the optic spectrum of absorption of four bands of the CaF2, doped with rare-earth ions or Yttrium was observed. To analyze the photochromic conduct of this monocrystal, irradiations with ultraviolete light were realized, verifying the reversible character of these centers. Through this experiment, the dependence of the transition 4D sub (3/2) of the ion Nd3+ with the band centered in 4.57 eV was verified. This band was identified as being due to the Center PC (photochromic center). The phosphorescence of the sample was measured after the irradiation-X, identifying it as being due to the ions Nd3+. (Author)